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DLLs are Simple! Part 3

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30 Sep 20042 min read 233.7K   5.9K   110   29
This article describes how to create a DLL with a DEF file and use it.

Introduction

In the third part of the assortment of articles "DLLs are Simple!" I describe how to create a DLL using a DEF file. What is a DEF file? It is a module-definition (*.def) file that is a text file containing one or more module statements that describe various attributes of a DLL, including:

LIBRARY statement statement identifies the DEF file as belonging to a DLL
EXPORTS statement lists the names of the functions exported by the DLL
DESCRIPTION statement describes the purpose of the DLL (optional)
C++
LIBRARY      "DefExported"
DESCRIPTION  'DefExported For Present in CodeProject'
EXPORTS
   Multiply @1

How to Build a DLL Using a DEF File

  1. Run VC++.
  2. Choose File>New.
  3. In the dialog box, choose "MFC AppWizard (DLL)" and name it, e.g. DefExported.
  4. Declare a member function:
    C++
    public:
     int Multiply(int PartOne,int PartTwo);
     CDefExportedApp();
  5. Then define it:
    C++
    int CDefExportedApp::Multiply(int PartOne, int PartTwo)
    {
     return PartOne*PartTwo;
    }
  6. In the FileView tab, click "Source Files" and double click on DefExported.def.
  7. After the EXPORT statement, enter [function name] @[number] like this:
    C++
    LIBRARY      "DefExported"
    DESCRIPTION  'DefExported For Present in CodeProject'
    EXPORTS
     ; Explicit exports can go here
     Multiply @1
  8. Click the Build Button.
  9. Bring the DLL out of the oven!!

How to Use a DLL

To use a DLL dynamically, there are three simple API functions:

  • LoadLibrary ( [path of DLL] ) Loads a DLL into the process address, returning a handle to the DLL.
  • GetProcAddress ( [loaded library] , [function name] )
    Returns a handle of a function so that it can be used in your application.
  • FreeLibrary( [handle of loaded DLL] )
    Releases the memory allocated when the DLL was loaded.
  1. Run VC++.
  2. Choose from the menu File>New.
  3. In the dialog box, choose "MFC AppWizard (EXE)" and name it, e.g. DynamicLoad.
  4. Select "Dialog Based" and click the Finish button.
  5. Place a button control on the dialog and double click on it to create its click event.
  6. Before typing the code for the button click (BN_CLICKED) event, we must define a new function pointer with the correct number of parameters. This is done according to the parameters of the function we exported above.
    C++
    typedef int (CALLBACK* LPFNMLTPLY)(int,<span lang="en-us"> int);<span lang="en-us">
    <p>Sometimes you have to convert some variable types. For more information about this conversion, see Microsoft Support Article ID: <a href="http://support.microsoft.com/default.aspx?scid=kb;en-us;117428">Q117428</a>. </p>
  7. Enter the code for the button click event:
    C++
    HINSTANCE hClcltr=LoadLibrary("DefExported.dll");
    LPFNMLTPLY lpfnMuliply;
    lpfnMuliply = (LPFNMLTPLY)GetProcAddress(hClcltr,"Multiply");
  8. Now we can use the Multiply function by calling lpfnMultiply and storing the return value.
    C++
    m_Rslt=lpfnMuliply(m_PartOne,m_PartTwo);
  9. When you are finished using the library, you must call the FreeLibrary API to release the memory allocated from the LoadLibrary method.
    C++
    FreeLibrary( hClcltr );

History

  • 30 September, 2004 -- Original version posted

License

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Written By
Web Developer
Iran (Islamic Republic of) Iran (Islamic Republic of)
I born in tehran at 1975
and began programming with commodore 64
I established "Pishro Narmafzar Iran" Corporation in 2001.
i'm expert in VC++, VC#, MS SQL Server, ASP .NET & have developed :
1-Persian Photoshop (fully localized)
2-Persian Freehand (fully localized)
3-Pardis (persian/arabic typing in graphical and video editing programs include : Ulead video studio,Ulead media studio,Pinnacle studio, Premiere, Flash, Freehand, 3D Max, Auto CAD, Photoshop, CorelDraw, Ulead Cool 3D,...)
Pardis is only persian/arabic typing tool for Ulead Video Studio in world.
Mahmoud komeily, mahmood komeili, محمود کمیلی

Comments and Discussions

 
QuestionWhere to put MFCAppWizard(exe) codes? Pin
xlav22217-Jul-06 13:55
xlav22217-Jul-06 13:55 

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